This section is from the book "Safe Building", by Louis De Coppet Berg. Also available from Amazon: Code Check: An Illustrated Guide to Building a Safe House.
Taking all things together, however, the superiority to-day for structural iron seems to lie with steel metal made under the Open Hearth process, (first introduced into this country by the New Jersey Steel and Iron Co.), because the results desired are under more perfect and intimate control. Ample opportunity is afforded at various stages of the process to test and duly correct the quality of the product, and a greater uniformity of the product itself seems to be obtained than with the other processes. For railway bars, Bessemer steel has at present largely the greater production being also cheaper and is undoubtedly well enough adapted to it, but for structural purposes, such as ships, bridges, roofs and girders, the best opinion today seems to incline to the preferment of the Open Hearth product on account of its superior uniformity.
But, as already emphasized several times, very little is really known to-day of the properties of steel and new tacts arc coming to light every day. It- manufacture and determination are undoubtedly still in their development, and though events point strongly to steel becoming the metal of the near future, there exists among many reasonably conservative men, a wide and well-grounded distrust of its use in the higher engineering or architectural structures, on account of its mysterious behavior, and frequent erratic and inexplicable failures. It should never be used, except after the most rigid and frequent tests, which of course add greatly to the expense attendant on its use.
Except that being cast in large masses requiring very heavy preliminary "breaking-down "or" blooming" mills to adapt it to the finishing strains, and that usually it is not piled, its subsequent manipulation to produce the ordinary structural forms is very similar to that already described for wrought-iron.
The ingot, while hot, is run to the blooming-mill, and there run through rollers to form the "blooms," which are each of the necessary weight in one piece, to make a whole beam or other shape. The cross-section of the bloom is about 3 inches by 9 inches, the length depending on the weight and length of beam or other shape desired, usually from 5 feet to 30 feet, the latter weighing a little over a ton each. These blooms occupy in the rolling of steel the corresponding place to the piled muck-bar or other iron in the rolling of iron.
The bloom is heated in a furnace and run through rollers, which gradually shape it to its final section, the same as with wrought-iron; the only difference being that the bloom is not heated to the same high temperature as iron, and, therefore, its resistance to squeezing when passing through the rolls is very much greater than with iron. Steel plants are, therefore, not only very expensive, but the amount of breakage in housings and rolls is very great.
The Phoenix Co. are preparing to make steel stock of similar size as from the iron muck-bars, and to pile them similarly. This will probably be done in time by all the mills, and may lead to a considerable saving in the expense of replacing broken machinery.
The writer understands that at present the Bessemer process is employed at the Homestead Works in Pittsburgh (Carnegie, Phipps & Co.) ; and by the Columbia Iron and Steel Co., of Uniontown, Pa.; and by the North Chicago Rolling-Mill Co., of Chicago; and that ingots made by the Open Hearth process are bought and used by the Passaic Rolling Mills, of Paterson, X. J., and by the New Jersey Steel and Iron Works, of Trenton, N. J. ; and that the latter also buy and use ingots made by the Bessemer process.
Use of Steel not yet commendable.
Rolling of Steel Bloom.
Processes used by Mills.
That the Clapp-Grilliths (modified Bessemer) process is used by the Pottsville Iron & Steel Co., of Pottsville, Pa.
The Siemens-Martin (Open Hearth) process is used by the Phoenix Iron Co., at Phcenixville, Pa., who roll their ingots ; and that the works now building for the Pencoyd Iron Works at Pencoyd, Pa., are also for the Open Hearth process, but that they intend to hammer their ingots.
These eight mills embrace all the leading mills in the United States where structural iron and steel of I-beam, channel, angle, deck-beam or tee-shapes are rolled.
A very cheap and inferior grade of steel, known as "puddled steel," is made by stopping the puddling of pig-iron before all the carbon is removed.
Many attempts have been made to establish exact lines of demarcation between wrought-iron, steel and cast-iron, but none are very satisfactory, though a few are here given.
Dr. Percy says if the iron be pure, contains no carbon, it is wrought-iron (though practically wrought-iron contains some 0,25 per cent of carbon). In this condition the iron is soft, tenacious, weldable, but not fusible.
If the iron contains some carbon, from 0,15 per cent to 1,8 per cent, it is steel, the different kinds of steel varying according to the quantity of carbon; the different steels being accordingly more or less elastic, malleable, forgeable, fusible and capable of hardening and tempering.
If the iron contains much carbon, from 2 per cent to 6 per cent, it is cast-iron and is hard, brittle and fusible, but it is neither weldable nor forgeable.
Table XXVII! (on page 26), does not, however, agree with what is called steel in American practice. Steel with 0,12 per cent of carbon is considered "mild steel," and with 0,36 per cent of carbon "hard steel." The former is used for structural purposes. Steel with more than 0,12 per cent of carbon will not stand the tests for the Government cruisers.
Classification of Irons and Steel.
The following (Table XXVIII) appeared originally in "Bauer-mann's Metallurgy."1